1. Field of the Invention
This invention relates to a radar equipment for vehicles in which a transmitting and a receiving antenna are arranged in a V-letter form.
2. Description of the Prior Art
A variety of radar equipments have been proposed for measurement of the distance between vehicles, detection of an obstacle standing ahead of them, and like purposes. A radar equipment of the type employing a V-shaped antenna, such as shown in FIG. 1, exhibits an advantage that it hardly suffers from radio wave interference by a vehicle running in the opposite direction. This V-shaped antenna comprises an edge shunt slots array antenna 1 and a longitudinal shunt slots array antenna 2 arranged in a V-letter form, a transmitter-receiver unit 3 provided at the link between the antennas 1 and 2, and semicylindrical parabolic reflectors 4 and 5 respectively mounted on the antennas 1 and 2. The plane of polarization of each antenna is inclined at an angle of 45.degree. relative to a perpendicular direction, and the resultant beam is a sharp pencil beam.
By using one of the antennas for transmitting use and the other for receiving use, their planes of polarization are displaced 90.degree. apart in relation to a vehicle running in the opposite direction, so that the V-shaped antenna is subjected to substantially no radio wave interference.
In the case of employing an FM-CW (Frequency Modulation Continuous Wave) radar, the arrangement shown in FIG. 2 may be adopted. In FIG. 2, reference character SA indicates a sending antenna; RA designates a receiving antenna; DCa and DCb identify directional couplers; Ra and Rb denote dummy loads; FMOSC represents a frequency modulator; MODOSC shows a modulation generator; MIX refers to a mixer; and AMP indicates an amplifier. The sending antenna SA and the receiving antenna RA constitute the V-shaped antenna shown in FIG. 1. By the directional coupler DCa provided between the frequency modulator FMOSC and the sending antenna SA, the output from the frequency modulator FMOSC is branched to the directional coupler DCb provided between the mixer MIX and the receiving antenna RA, and mixed with a received signal in the mixer MIX. The mixer output is amplified by the amplifier AMP to derive therefrom a beat output, and a frequency-modulated continuous wave is sent out from the sending antenna SA, and a reflected wave from an obstacle or the like is received by the receiving antenna RA, thereby to measure, with the output signal from the amplifier AMP, the distance to the obstacle or the speed relative to the vehicle loaded with the radar equipment.
The aperture planes of waveguides of the sending and receiving antennas SA and RA at the feeding point perpendicular intersect each other in the longitudinal direction of each waveguide; accordingly, it is necessary to employ a twist waveguide for coupling the both antennas so that they extend in parallel in their lengthwise direction. But, since the twist waveguide is relatively bulky, the transmitter-receiver unit disposed at the base of the V-shaped antenna cannot be reduced in size.